<html>

<body>
<script type="text/javascript">

function haha(me) {
    var form = document.forms['surprise'];
    var message = document.getElementById('message');
    if (form.elements['one'].checked &&
        form.elements['dos'].checked &&
        form.elements['san'].checked) {
        message.innerHTML = 'HAPPY BIRTHDAY!';
    }
    else {
        message.innerHTML = me.name;
        
    }
}

</script>

<form name="surprise">
    <input type="checkbox" name="one" onclick="haha(this);">one</input><br />
    <input type="checkbox" name="dos" onclick="haha(this);">dos</input><br />
    <input type="checkbox" name="san" onclick="haha(this);">san</input><br />
</form>

<div style="font-size: 50pt;" id="message"></div>

</body>

</html>
